Turnable foot for leg prostheses



'Dec. 13, 1949 u. K. HENSCHKE ET AL 2,490,806

TURNABLE FOOT FOR LEGEROSTHESES I Filed June 2, 1948 f .2 h mm ww W m; mflM @P/L/ K w y M N E 4 y w Patented Dec. 13, 1949 UNITED STATES OFFICE Application June 2, 1948, Serial No. 30,714

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) 8 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to us of any royalty thereon.

This invention relates to a turnable foot for artificial legs which provides lateral motion of the foot without decreasing the stability of the amputee using such a prosthesis.

In the field of artificial limbs, constructions became known in which the frontal part of the foot or the whole foot is made turnable about an axis running in the direction of the foot in order to simulate the natural lateral movement of the human foot. In these constructions, the turning movement occurs either freely, that means only with friction forces unavoidable in the standard bearing constructions, or the turning movement is furnished by springs or rubber bumpers with an increasing torque resistance. Both construction principles enable the amputee to walk better on uneven ground than with artificial legs without lateral movement of the foot. In the first of the above mentioned constructions, the stability towards the side is very small because no resistance against lateral tilting movements of the whole prosthesis can be exerted from the foot and is somewhat like walking on a knife edge. In the second type of construction, such forces are exerted and they increase with increasing lateral motion on the foot which places a lateral torque in the reverse direction on the amputee. Thus the advantages achieved by the turnable foot are partly abolished because the forces arising in the foot tend to tilt the foot according to the lateral inclination of the ground.

The present invention aims at the removal of these disadvantages by achieving an adjustment of the foot to each required lateral position and at a fixation of the foot in this position when the amputee passes the body weight over his leg. The technical principle on which the invention is based consists in producing friction forces in the bearing for the lateral foot movement by body weight being placed on the ball of the foot. The friction forces act against further lateral turning movements of the foot and eliminate any sidewise moments being exerted on the amputee tending to throw him off balance.

The constructive realization of this idea depends on the kind of bearing construction which might be preferred in a special case. Two types of bearing surfaces are considered preferred, that a cylindrical bearing surface and that of a disk-like bearing surface. According to the invention, the forces necessary for producing the friction are created in either of the two types by the installation of bearing surfaces for lateral foot movement behind the ball of the foot towards the heel. By these installations, a bending moment is produced due to forces originated by the amputees weight on the ball of the foot. This bending moment acts on the bearing to bind the bearing against further turning movement. The more the bearing is away from the ball of the foot towards the heel the stronger will be the bending moment and consequently the greater will be the friction in the bearing. The choice of those dimensions depends upon whether one wants to make the bearing selflockin or only frictionally braked. In a bearing construction with cylindrical bearing surfaces, thefrictional forces can be further increased by using a cylindrical bearing surface of relatively large bearing diameter and of relatively short bearing length.

It is a primary object of this invention to provide a turnable foot for leg prostheses capable of orienting itself laterally to the contour of the supporting earth and becoming stable in this position under weight whereby the balance of the amputee is maintained.

It is another object of this invention to provide an artificial leg having a foot which has the toe portion laterally rotatable to permit it to freely position itself on uneven ground and be frictionally stabilized in that position when weight is placed on the ball of the foot to stabilize the amputee during walking.

A further object of this invention is to provide a foot for artificial legs in which the ball of the foot is rotatably mounted on the foot by a bearing having cooperative frictional elements on the two bearing parts that frictionally hold the ball of the foot in any angular position by applied pressure on the ball of the foot to enable an amputee to walk on rough or slanting ground without introducing lateral forces or movements on the foot or leg.

These and other objects will become more apparent as the description proceeds when taken in 3 element l that is attached to the shank II by an ankle joint of any well known type. The foot element It is produced in two sections, the heel I 2 and the toe l3. These two sections are connected by a bearing which permits the toe section to rotate with respect to the heel section about an axis running in the direction of the foot. In the foot section i3 is a bolt l4 having a flanged portion l5 approximately midway thereof that rests in a slight companion depression on the back wall l6 of the foot section. The forward end of the bolt 14 is square at H, or otherwise irregularly shaped, to provide a nonrotatable joint with a bracket member l8 fastened by screws 19, or other well known means,

and recessed in the toe section. The bracket member [8 has a short extension through which is a square hole receiving the -squared'portion of the bolt M. A hole is drilled through the extension 20 and the squared portion I1 and a *c'otter'pin 21 inserted therethrough to retain the bolt in the toe section.

Backwardly of the flanged portion 15 of the bolt H3 is a squared or otherwise polygonal portion 22 that extends to a threaded portion 23. A

flanged collar 24 having an opening companion to the portion 22 of the bolt is slipped over the bolt M such that the unfianged end of the collar 24 rests against the flange i5 and is held securely in place over the portion 22 by a nut 25 threaded on the threaded portion 23 of the bolt l4.

The heel section 12 of the foot .is turned inwardly to form a front wall 26 through which is an openin 2.! that is freely slidable and rotatable over the collar 24 between the collar flange and the back wall to of the toe section. Between the collar flange 24 and the wall 26 is a friction washer 28 that encircles the collar 25. Between the wall 26 of the heel section and the back wall it of the toe section are two friction washers 29 and 30 with an interposed metallic Washer 31. It is preferable that the friction washers 29 and 30 be cemented or otherwise attached to the walls i6 and 26, respectively, to e a insure slip between the washers 29 and 3| or 3i and 3|. The distance across the washers 28, 29, 39, 3| and the Wall 26 is slightly less than the distance from the collar flange 24 and the wall l6 of the toe section which enables the toe section to rotate freely when there are no strains-or forces acting on this toe section normal to its axis of rotation. Upon the toe section being subjected to lateral forces, as by the iamputeeplacing weight on the ball of the foot, the toe section l3 will product a binding force between the-collar flange 2t and the wall 26 under th bolt 14 and also a binding force between the wall 15 and th wall 26 above the bolt l4 proportional to the lateral forces-on the toe section.

For the purpose of explanation of operation, let it be assumed that an amputee using an artificial limb with such a turnable foot is walking over rough ground. As the amputee puts the heel of the prosthesis on the ground, the shoe on the foot of the prosthesis will turn later-ally about the longitudinal axis of the foot until the sole of the shoe and the ground meet squarely. By this rotary movement of the shoe, the toe part of the foot of the prosthesis will be turned also. Durin this movement, .no friction forces will occur within the'bearing, which connect the toe and heel sections of the foot, because no noticeable pressure will be exerted on the ball of the foot. The continuing movement of the iii) 4 amputees body over the leg puts the weight more and mor on the ball of the foot producing a bending moment at the bearing to frictionally bind diametrically opposite portions of the friction washers frictionally stabilizing the toe section in this position. The amputee will therefore feel no lateral strains on the leg and consequently will require no balance readjusting of his body. Actually such foot action operates to stabilize the amputee. Taking the weight off the foot releases the toe section for free rotation to meet the earth flatly on the next succeeding step. The shoe worn on this turnable foot will limit the rotational movement of the toe section with respect to the heel section but stops may be placed on the two sections to positively limit their relative rotational movement in any well known "and expedient manner. I

Another simple and efiective means of frictionally holding the toe section of a turnable foot is shown in Fig. 2 in which like parts are designated with the same reference characters :as used in Fig. 1 and other reference characters are primed which designate corresponding 'elements of Fig. '1. Within the toe section 13" is a cup-shaped member having a cylindrical wall 58 and a base 5| set in a cylindrical recess of the toe section and retained therein by screws 52. Fixed integrally :and concentrically with the base 5! is a stud 53 standing upwardly in the cup having threads 'onithe outer'end thereof.

On the front of the heel section 12' .is a cupshaped member having a cylindrical Wall-54 with an outstanding flange 55 welded :or otherwise fastened to the front wall 25 of the heel section. The cylinder 55 has a base '55 with a central opening 51 that loosely passes over the stud 5-3 and is retained by a washer 58 and a nut 59 keyed by a cotter pin to such that the cylinder it remains within the cup-shaped cylinder 50. The cylindrical member '54 has a very slight clearance with the cylinder wall '50 and the base of the "cylindrical member 54 is free to travel a slight a-mount along the stud 53 such that lateral pressures, usually on the ball of the foot will cause a bending moment in the connected parts to produce a binding friction 'on the cylindrical surfaces 50, 54.

The interfitting companion cup-shaped cylindrical members produce the same function and results as the disk clutch means shown and described for Fig. l and it is therefore not believed necessary to proceed with a description of operation. The toe section of the foot being turnable and frictionally held when weight isapplied on the ball of the foot gives the amputee much more assurance when walking over rough terrain and he is less apt to stumble and lose his balance.

To ease the rotary movement of the shoe about the longitudinal axis of the foot, the toe section may have a shell-like extension 18 to the rear, as is shown in Fig. 3, which fits with-some-clearance over the heel section [2 of the foot, this bed section being shaped such as to allow for an unobstructed lateral rotation of the shell-like extension about it within the necessary angle and at the same time limiting this rotation.

It has probably become quite apparent in view of the aboveclcscriptionthat various changes and modifications can be made to produce substantially the same results and functions as by using a conical friction clutch bearing 'or a toothed clutch bearingorother type-clutch bearing means in place of a disk or cylindrical clutch bearing shown and described. While various changes in construction can be made without departing from the spirit and the scope of this invention, we desire to be limited only by the scope of the appended claims.

We claim:

1. A turnable foot for artificial legs comprising a toe section having a hollow shell-like heel portion and a heel section substantially enclosed within the shell-like heel portion of said toe section, said toe and heel sections being rotatively held together by a bearing element on an axis lying in a direction of the foot, the bearing element having portions thereon adaptable to hold said bearing element from relative rotation of the toe and heel sections upon lateral forces being exerted on said toe section. V

2. A turnable foot for artificial legs comprising a foot section and a toe section having companion adjacent faces, one of, said faces having a stud extending therefrom and extending through the face of the other to Irotatively retain said toe and heel sections together; and friction washers interposed between said faces encircling said stud with a slight clearance to permit free rotation of said'toe, section with respect to said heel section in the presence of a rotational force and in the absence of a lateral force on said toe section and to restrict rotative movement of said toe section with respect to said heel section when said toe section is sub jected to lateral forces.

3. A turnable foot for artificial legs comprising a heel section adaptable to be connected to a leg shank and a toe section rotatably and substantially nonaxially movably connected loosely to the forward part of the heel section behind the ball of the. foot on an axis running in the direction of the foot and centrally thereof; and a frictional disk clutch means interposed between said toe and heel sections that is disengaged in the absence of any lateral forces acting on the toe section and is engaged upon lateral thrusts exerted on the toe section whereby an amputee using the turnable foot is able to walk jacent surfaces; an inwardly directed cylindrical cup-shaped member fixed in the companion surface of said toe section; an outwardly directed cylindrical cup-shaped member fixed to the companion surface of said heel section, said second mentioned cup-shaped member being positioned within said first mentioned cup-shaped member, the outer diameter of said second mentioned cup-shaped member being slightly less than the inner diameter of said first mentioned cup-shaped member; and a pin means centrally through the bottom walls of said cup-shaped members for retaining said toe and heel sections relatively rotational and axially inseparable.

6 A rotatable foot for artificial legs as set forth in claim 4 wherein said toe section has a shell-like heel extension substantially enclosing said heel section for holding a shoe placed thereonout of contact with said heel section.

,7. A rotatable foot for artificial legs as set forth in claim 6 wherein said toe section has a shelllikeheel extension substantially enclosing said heel; section for holding a shoe placed thereon out-,of contact with said heel section.

.8. ;A turnable foot for artificial legs comprising a heel section and a toe section including the ballv of the foot joined with adjacent portions thereof in contiguous relation by a connecting 'element operative on an axis running in the direction of the foot to permit rotation and section around said axis, the clutch engageable 5 surfaces being sufficiently disengaged to allow free rotation of the toe section with respect to the heel section to permit positioning of the toe section on the supporting surface in the presence of a rotational force and the absence of a lateral force on said toe section and the clutch engageable surfaces being engageable upon a lateral force being placed on said toe section to hold said toe section against rotation with on slanting or rough ground without producing undesirable sidewise moments on the amputee's body.

4. A turnable foot for artificial legs comprising cup-shaped members whereby lateral pressures on the toe section of said foot produces a bind:

ing friction in proportion to the applied pressure to frictionally stabilize the toe section against rotation with respect to the heel section.

5. A rotatable foot for artificial legs comprising toe and heel sections having companion adrespect to said heel section whereby said toe section does not produce a rotative torque on said heel section during the stepping process on irregular supporting surfaces.

ULRICH K. HENSCHKE.

HANS A. MAUCH.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,495,588 Habermann May 27, 1924 FOREIGN PATENTS Number Country Date 138,278 Great Britain Feb. 5, 1920 315,948 Germany Dec. 3, 1919 i 392,0'80 Germany Mar. 20, 1924 

